Lithographic apparatus and method

ABSTRACT

A lithographic apparatus is disclosed that includes a substrate table configured to support a substrate on a substrate supporting area and a heater and/or temperature sensor on a surface adjacent the substrate supporting area.

This application is a continuation of co-pending U.S. Pat. ApplicationNo. 17/698,100, filed Mar. 18, 2022, which is a continuation of U.S.Pat. Application No. 16/734,579, filed on Jan. 6, 2020, now U.S. Pat.No. 11,281,115, which is a continuation of U.S. Pat. Application No.13/046,283, filed on Mar. 11, 2011, now U.S. Pat. No. 10,551,752, whichclaims priority and benefit under 35 U.S.C. §119(e) to U.S. ProvisionalPat. Application No. 61/313,410, filed on Mar. 12, 2010, to U.S.Provisional Pat. Application No. 61/354,126, filed on Jun. 11, 2010, toU.S. Provisional Pat. Application No. 61/384,666, filed on Sep. 20,2010, and to U.S. Provisional Pat. Application No. 61/416,142, filed onNov. 22, 2010. The content of each of the foregoing applications isincorporated herein in its entirety by reference.

FIELD

The present description relates to a lithographic apparatus and a methodof compensating for local heat load variations.

BACKGROUND

A lithographic apparatus is a machine that applies a desired patternonto a substrate, usually onto a target portion of the substrate. Alithographic apparatus can be used, for example, in the manufacture ofintegrated circuits (ICs). In that instance, a patterning device, whichis alternatively referred to as a mask or a reticle, may be used togenerate a circuit pattern to be formed on an individual layer of theIC. This pattern can be transferred onto a target portion (e.g.comprising part of, one, or several dies) on a substrate (e.g. a siliconwafer). Transfer of the pattern is typically via imaging onto a layer ofradiation-sensitive material (resist) provided on the substrate. Ingeneral, a single substrate will contain a network of adjacent targetportions that are successively patterned. Known lithographic apparatusinclude so-called steppers, in which each target portion is irradiatedby exposing an entire pattern onto the target portion at one time, andso-called scanners, in which each target portion is irradiated byscanning the pattern through a radiation beam in a given direction (the“scanning”-direction) while synchronously scanning the substrateparallel or anti-parallel to this direction. It is also possible totransfer the pattern from the patterning device to the substrate byimprinting the pattern onto the substrate.

It has been proposed to immerse the substrate in the lithographicprojection apparatus in a liquid having a relatively high refractiveindex, e.g. water, so as to fill a space between the final element ofthe projection system and the substrate. In an embodiment, the liquid isdistilled water, although another liquid can be used. An embodiment ofthe present invention will be described with reference to liquid.However, another fluid may be suitable, particularly a wetting fluid, anincompressible fluid and/or a fluid with higher refractive index thanair, desirably a higher refractive index than water. Fluids excludinggases are particularly desirable. The point of this is to enable imagingof smaller features since the exposure radiation will have a shorterwavelength in the liquid. (The effect of the liquid may also be regardedas increasing the effective numerical aperture (NA) of the system andalso increasing the depth of focus.) Other immersion liquids have beenproposed, including water with solid particles (e.g. quartz) suspendedtherein, or a liquid with a nano-particle suspension (e.g. particleswith a maximum dimension of up to 10 nm). The suspended particles may ormay not have a similar or the same refractive index as the liquid inwhich they are suspended. Other liquids which may be suitable include ahydrocarbon, such as an aromatic, a fluorohydrocarbon, and/or an aqueoussolution.

Submersing the substrate or substrate and substrate table in a bath ofliquid (see, for example U.S. Pat. No. US 4,509,852) means that there isa large body of liquid that must be accelerated during a scanningexposure. This requires additional or more powerful motors andturbulence in the liquid may lead to undesirable and unpredictableeffects.

One of the arrangements proposed is for a liquid supply system toprovide liquid on only a localized area of the substrate and in betweenthe final element of the projection system and the substrate using aliquid confinement system (the substrate generally has a larger surfacearea than the final element of the projection system). One way which hasbeen proposed to arrange for this is disclosed in PCT patent applicationpublication no. WO 99/49504. As illustrated in FIGS. 2 and 3 , liquid issupplied by at least one inlet IN onto the substrate, preferably alongthe direction of movement of the substrate relative to the finalelement, and is removed by at least one outlet after having passed underthe projection system. That is, as the substrate is scanned beneath theelement in a -X direction, liquid is supplied at the +X side of theelement and taken up at the -X side. FIG. 2 shows the arrangementschematically in which liquid is supplied via inlet and is taken up onthe other side of the element by outlet which is connected to a lowpressure source. In the illustration of FIG. 2 the liquid is suppliedalong the direction of movement of the substrate relative to the finalelement, though this does not need to be the case. Various orientationsand numbers of in- and out-lets positioned around the final element arepossible, one example is illustrated in FIG. 3 in which four sets of aninlet with an outlet on either side are provided in a regular patternaround the final element. Arrows in liquid supply and liquid recoverydevices indicate the direction of liquid flow.

A further immersion lithography solution with a localized liquid supplysystem is shown in FIG. 4 . Liquid is supplied by two groove inlets oneither side of the projection system PS and is removed by a plurality ofdiscrete outlets arranged radially outwardly of the inlets. The inletsand can be arranged in a plate with a hole in its center and throughwhich the projection beam is projected. Liquid is supplied by one grooveinlet on one side of the projection system PS and removed by a pluralityof discrete outlets on the other side of the projection system PS,causing a flow of a thin film of liquid between the projection system PSand the substrate W. The choice of which combination of inlet andoutlets to use can depend on the direction of movement of the substrateW (the other combination of inlet and outlets being inactive). In thecross-sectional view of FIG. 4 , arrows illustrate the direction ofliquid flow in inlets and out of outlets.

In European patent application publication no. EP 1420300 and U.S. Pat.application publication No. US 2004-0136494, the idea of a twin or dualstage immersion lithography apparatus is disclosed. Such an apparatus isprovided with two tables for supporting a substrate. Levelingmeasurements are carried out with a table at a first position, withoutimmersion liquid, and exposure is carried out with a table at a secondposition, where immersion liquid is present. Alternatively, theapparatus has only one table.

PCT patent application publication WO 2005/064405 discloses an all wetarrangement in which the immersion liquid is unconfined. In such asystem the whole top surface of the substrate is covered in liquid. Thismay be advantageous because then the whole top surface of the substrateis exposed to the substantially same conditions. This has an advantagefor temperature control and processing of the substrate. In WO2005/064405, a liquid supply system provides liquid to the gap betweenthe final element of the projection system and the substrate. Thatliquid is allowed to leak over the remainder of the substrate. A barrierat the edge of a substrate table prevents the liquid from escaping sothat it can be removed from the top surface of the substrate table in acontrolled way. Although such a system improves temperature control andprocessing of the substrate, evaporation of the immersion liquid maystill occur. One way of helping to alleviate that problem is describedin United States Pat. application publication No. US 2006/0119809. Amember is provided which covers the substrate W in all positions andwhich is arranged to have immersion liquid extending between it and thetop surface of the substrate and/or substrate table which holds thesubstrate.

SUMMARY

Because of the presence of liquid on the substrate in an immersionlithographic apparatus, evaporational heat loads can result on one ormore components which come into contact with immersion liquid (e.g. thesubstrate and/or substrate table). These heat loads can lead to thermalexpansion and/or contraction. Such thermal expansion and/or contractioncan lead to imaging errors, in particular overlay errors.

It is desirable, for example, to provide an apparatus in which theoccurrence of thermal expansion/contraction effects are reduced. Inparticular it is desirable to provide a system configured to reducethermal expansion/contraction effects in an immersion system which usesa supply system which provides immersion fluid to a localized area ofthe substrate and/or substrate table.

According to an aspect of the invention, there is provided alithographic apparatus comprising: a heater and/or temperature sensor ona surface.

According to an aspect of the invention, there is provided a substratetable configured to support a substrate on a substrate supporting area,the substrate table comprising a plurality of heaters and/or temperaturesensors adjacent a central portion of the substrate supporting area, theplurality of heaters and/or sensors being elongate.

According to an aspect of the invention, there is provided alithographic apparatus comprising: a substrate table configured tosupport a substrate on a substrate supporting area and comprising aheater and/or a temperature sensor which extends across the substratesupporting area from one edge to an opposite edge.

According to an aspect of the invention, there is provided alithographic apparatus, wherein the surface is a surface on a substratetable configured to support a substrate on a substrate supporting areawhich is: adjacent the substrate supporting area, or adjacent a sensoror adjacent a swap bridge.

According to an aspect of the invention, there is provided a substratetable configured to support a substrate on a substrate supporting areaand a heater and/or temperature sensor on a surface adjacent thesubstrate supporting area.

According to an aspect of the invention, there is provided a method ofcompensating for a local heat load in an immersion lithographicprojection apparatus the method comprising: controlling a heater orusing a signal from a temperature sensor to compensate for a local heatload wherein the heater and/or temperature sensor is on a surface.

According to an aspect of the invention, there is provided alithographic apparatus comprising an electrically conductive coating ona surface, and a heater and/or temperature sensor connected to thecoating.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will now be described, by way of exampleonly, with reference to the accompanying schematic drawings in whichcorresponding reference symbols indicate corresponding parts, and inwhich:

FIG. 1 depicts a lithographic apparatus according to an embodiment ofthe invention;

FIGS. 2 and 3 depict a liquid supply system for use in a lithographicprojection apparatus;

FIG. 4 depicts a further liquid supply system for use in a lithographicprojection apparatus;

FIG. 5 depicts, in cross-section, a barrier member which may be used inan embodiment of the present invention as a liquid supply system;

FIG. 6 illustrates, in cross-section, another barrier member which maybe used in an embodiment of the present invention;

FIG. 7 illustrates, in cross-section, a portion of a substrate tablesurrounding the edge of a substrate;

FIG. 8 illustrates, in plan, a central section of a substrate table;

FIG. 9 illustrate, in cross-section, a burl plate showing the locationof heaters and/or temperature sensors;

FIG. 10 illustrates, in plan, heaters and/or temperature sensors in acentral portion of a substrate supporting area and edge heaters adjacentdifferent portions of an edge of the substrate supporting area;

FIG. 11 illustrates, in plan, an embodiment without edge heaters andalso illustrates a meander path which the substrate support may takeunder the projection system;

FIG. 12 is a schematic drawing illustrating the construction of a heaterand temperature sensor, in plan;

FIG. 13 is a schematic drawing illustrating the construction of a heaterand/or temperature sensor, in plan;

FIG. 14 is a schematic drawing illustrating the construction of a heaterand/or temperature sensor, in plan;

FIG. 15 is a schematic drawing illustrating the construction of a heaterand a temperature sensor, in plan;

FIG. 16 is a schematic drawing illustrating the construction of amicro-electro-mechanical system (MEMS) heater/sensor, in cross-section;

FIG. 17 is a detail of FIG. 16 showing the operation of the sensor;

FIG. 18 is a graph illustrating the variation of resistance on the Yaxis versus temperature on the X axis for an EM-temperature basedself-regulating heater;

FIG. 19 is a schematic drawing illustrating the construction of anEM-temperature based self-regulating heater, in cross-section;

FIG. 20 is a perspective view of an arrangement of EM-temperature basedself-regulating heaters;

FIG. 21 is a schematic drawing, in plan, illustrating where heatersand/or temperature sensors may be placed on a substrate table;

FIG. 22 is a schematic drawing, in cross-section, illustrating whereheaters and/or temperature sensors may be placed;

FIG. 23 is a schematic side-view drawing illustrating a temperaturesensor;

FIG. 24 is a schematic side-view drawing illustrating a temperaturesensor;

FIG. 25 is a schematic drawing, in plan, illustrating the temperaturesensor of FIG. 24 ;

FIG. 26 is a schematic drawing, in cross-section, illustrating whereheaters and/or temperature sensors may be placed;

FIG. 27 is a graph illustrating the effectiveness of a thin film heaterand/or temperature sensor;

FIG. 28 is a schematic drawing, in plan, illustrating a mask that may beused to deposit a thin film heater and/or temperature sensor;

FIG. 29 is a schematic drawing, in cross-section, illustrating whereheaters and/or temperature sensors may be placed;

FIG. 30 is a schematic drawing, in cross-section, illustrating whereheaters and/or temperature sensors may be placed; and

FIG. 31 is a schematic drawing, in plan, illustrating where temperaturesensors may be placed.

DETAILED DESCRIPTION

FIG. 1 schematically depicts a lithographic apparatus according to oneembodiment of the invention. The apparatus comprises:

-   an illumination system (illuminator) IL configured to condition a    radiation beam B (e.g. UV radiation or DUV radiation);-   a support structure (e.g. a mask table) MT constructed to support a    patterning device (e.g. a mask) MA and connected to a first    positioner PM configured to accurately position the patterning    device in accordance with certain parameters;-   a substrate table (e.g. a wafer table) WT constructed to hold a    substrate (e.g. a resist-coated wafer) W and connected to a second    positioner PW configured to accurately position the substrate in    accordance with certain parameters; and-   a projection system (e.g. a refractive projection lens system) PS    configured to project a pattern imparted to the radiation beam B by    patterning device MA onto a target portion C (e.g. comprising one or    more dies) of the substrate W.

The illumination system may include various types of optical components,such as refractive, reflective, magnetic, electromagnetic, electrostaticor other types of optical components, or any combination thereof, fordirecting, shaping, or controlling radiation.

The support structure MT holds the patterning device. The supportstructure MT holds the patterning device in a manner that depends on theorientation of the patterning device, the design of the lithographicapparatus, and other conditions, such as for example whether or not thepatterning device is held in a vacuum environment. The support structureMT can use mechanical, vacuum, electrostatic or other clampingtechniques to hold the patterning device. The support structure MT maybe a frame or a table, for example, which may be fixed or movable asrequired. The support structure MT may ensure that the patterning deviceis at a desired position, for example with respect to the projectionsystem. Any use of the terms “reticle” or “mask” herein may beconsidered synonymous with the more general term “patterning device.”

The term “patterning device” used herein should be broadly interpretedas referring to any device that can be used to impart a radiation beamwith a pattern in its cross-section such as to create a pattern in atarget portion of the substrate. It should be noted that the patternimparted to the radiation beam may not exactly correspond to the desiredpattern in the target portion of the substrate, for example if thepattern includes phase-shifting features or so called assist features.Generally, the pattern imparted to the radiation beam will correspond toa particular functional layer in a device being created in the targetportion, such as an integrated circuit.

The patterning device may be transmissive or reflective. Examples ofpatterning devices include masks, programmable mirror arrays, andprogrammable LCD panels. Masks are well known in lithography, andinclude mask types such as binary, alternating phase-shift, andattenuated phase-shift, as well as various hybrid mask types. An exampleof a programmable mirror array employs a matrix arrangement of smallmirrors, each of which can be individually tilted so as to reflect anincoming radiation beam in different directions. The tilted mirrorsimpart a pattern in a radiation beam which is reflected by the mirrormatrix.

The term “projection system” used herein should be broadly interpretedas encompassing any type of projection system, including refractive,reflective, catadioptric, magnetic, electromagnetic and electrostaticoptical systems, or any combination thereof, as appropriate for theexposure radiation being used, or for other factors such as the use ofan immersion liquid or the use of a vacuum. Any use of the term“projection lens” herein may be considered as synonymous with the moregeneral term “projection system”.

As here depicted, the apparatus is of a transmissive type (e.g.employing a transmissive mask). Alternatively, the apparatus may be of areflective type (e.g. employing a programmable mirror array of a type asreferred to above, or employing a reflective mask).

The lithographic apparatus may be of a type having two (dual stage) ormore substrate tables (and/or two or more patterning device tables). Insuch “multiple stage” machines the additional tables may be used inparallel, or preparatory steps may be carried out on one or more tableswhile one or more other tables are being used for exposure.

Referring to FIG. 1 , the illuminator IL receives a radiation beam froma radiation source SO. The source and the lithographic apparatus may beseparate entities, for example when the source is an excimer laser. Insuch cases, the source is not considered to form part of thelithographic apparatus and the radiation beam is passed from the sourceSO to the illuminator IL with the aid of a beam delivery system BDcomprising, for example, suitable directing mirrors and/or a beamexpander. In other cases the source may be an integral part of thelithographic apparatus, for example when the source is a mercury lamp.The source SO and the illuminator IL, together with the beam deliverysystem BD if required, may be referred to as a radiation system.

The illuminator IL may comprise an adjuster AD configured to adjust theangular intensity distribution of the radiation beam. Generally, atleast the outer and/or inner radial extent (commonly referred to asσ-outer and σ-inner, respectively) of the intensity distribution in apupil plane of the illuminator can be adjusted. In addition, theilluminator IL may comprise various other components, such as anintegrator IN and a condenser CO. The illuminator may be used tocondition the radiation beam, to have a desired uniformity and intensitydistribution in its cross-section. Similar to the source SO, theilluminator IL may or may not be considered to form part of thelithographic apparatus. For example, the illuminator IL may be anintegral part of the lithographic apparatus or may be a separate entityfrom the lithographic apparatus. In the latter case, the lithographicapparatus may be configured to allow the illuminator IL to be mountedthereon. Optionally, the illuminator IL is detachable and may beseparately provided (for example, by the lithographic apparatusmanufacturer or another supplier).

The radiation beam B is incident on the patterning device (e.g., mask)MA, which is held on the support structure (e.g., mask table) MT, and ispatterned by the patterning device. Having traversed the patterningdevice MA, the radiation beam B passes through the projection system PS,which focuses the beam onto a target portion C of the substrate W. Withthe aid of the second positioner PW and position sensor IF (e.g. aninterferometric device, linear encoder or capacitive sensor), thesubstrate table WT can be moved accurately, e.g. so as to positiondifferent target portions C in the path of the radiation beam B.Similarly, the first positioner PM and another position sensor (which isnot explicitly depicted in FIG. 1 ) can be used to accurately positionthe patterning device MA with respect to the path of the radiation beamB, e.g. after mechanical retrieval from a mask library, or during ascan. In general, movement of the support structure MT may be realizedwith the aid of a long-stroke module (coarse positioning) and ashort-stroke module (fine positioning), which form part of the firstpositioner PM. Similarly, movement of the substrate table WT may berealized using a long-stroke module and a short-stroke module, whichform part of the second positioner PW. In the case of a stepper (asopposed to a scanner) the support structure MT may be connected to ashort-stroke actuator only, or may be fixed. Patterning device MA andsubstrate W may be aligned using patterning device alignment marks M1,M2 and substrate alignment marks P1, P2. Although the substratealignment marks as illustrated occupy dedicated target portions, theymay be located in spaces between target portions (these are known asscribe-lane alignment marks). Similarly, in situations in which morethan one die is provided on the patterning device MA, the patterningdevice alignment marks may be located between the dies.

The depicted apparatus could be used in at least one of the followingmodes:

1. In step mode, the support structure MT and the substrate table WT arekept essentially stationary, while an entire pattern imparted to theradiation beam is projected onto a target portion C at one time (i.e. asingle static exposure). The substrate table WT is then shifted in the Xand/or Y direction so that a different target portion C can be exposed.In step mode, the maximum size of the exposure field limits the size ofthe target portion C imaged in a single static exposure.

2. In scan mode, the support structure MT and the substrate table WT arescanned synchronously while a pattern imparted to the radiation beam isprojected onto a target portion C (i.e. a single dynamic exposure). Thevelocity and direction of the substrate table WT relative to the supportstructure MT may be determined by the (de)magnification and imagereversal characteristics of the projection system PS. In scan mode, themaximum size of the exposure field limits the width (in the non-scanningdirection) of the target portion in a single dynamic exposure, whereasthe length of the scanning motion determines the height (in the scanningdirection) of the target portion.

3. In another mode, the support structure MT is kept essentiallystationary holding a programmable patterning device, and the substratetable WT is moved or scanned while a pattern imparted to the radiationbeam is projected onto a target portion C. In this mode, generally apulsed radiation source is employed and the programmable patterningdevice is updated as required after each movement of the substrate tableWT or in between successive radiation pulses during a scan. This mode ofoperation can be readily applied to maskless lithography that utilizesprogrammable patterning device, such as a programmable mirror array of atype as referred to above.

Combinations and/or variations on the above described modes of use orentirely different modes of use may also be employed.

Arrangements for providing liquid between a final element of theprojection system PS and the substrate can be classed into two generalcategories. These are the bath type arrangement in which the whole ofthe substrate W and optionally part of the substrate table WT issubmersed in a bath of liquid and the so called localized immersionsystem which uses a liquid supply system in which liquid is onlyprovided to a localized area of the substrate. In the latter category,the space filled by liquid is smaller in plan than the top surface ofthe substrate and the area filled with liquid remains substantiallystationary relative to the projection system PS while the substrate Wmoves underneath that area. A further arrangement, to which anembodiment of the present invention is directed, is the all wet solutionin which the liquid is unconfined. In this arrangement substantially thewhole top surface of the substrate and all or part of the substratetable is covered in immersion liquid. The depth of the liquid coveringat least the substrate is small. The liquid may be a film, such as athin film, of liquid on the substrate. Any of the liquid supply devicesof FIGS. 2-5 may be used in such a system; however, sealing features arenot present, are not activated, are not as efficient as normal or areotherwise ineffective to seal liquid to only the localized area. Fourdifferent types of localized liquid supply systems are illustrated inFIGS. 2-5 . The liquid supply systems disclosed in FIGS. 2-4 weredescribed above.

Another arrangement which has been proposed is to provide the liquidsupply system with a liquid confinement member which extends along atleast a part of a boundary of the space between the final element of theprojection system and the substrate table. Such an arrangement isillustrated in FIG. 5 . The liquid confinement member is substantiallystationary relative to the projection system in the XY plane thoughthere may be some relative movement in the Z direction (in the directionof the optical axis). A seal is formed between the liquid confinementand the surface of the substrate. In an embodiment, a seal is formedbetween the liquid confinement structure and the surface of thesubstrate and may be a contactless seal such as a gas seal. Such asystem is disclosed in U.S. Pat. application publication No. US2004-0207824.

FIG. 5 schematically depicts a localized liquid supply system with abarrier member 12, IH. The barrier member extends along at least a partof a boundary of the space between the final element of the projectionsystem and the substrate table WT or substrate W. (Please note thatreference in the following text to surface of the substrate W alsorefers in addition or in the alternative to a surface of the substratetable, unless expressly stated otherwise.) The barrier member 12 issubstantially stationary relative to the projection system in the XYplane though there may be some relative movement in the Z direction (inthe direction of the optical axis). In an embodiment, a seal is formedbetween the barrier member and the surface of the substrate W and may bea contactless seal such as a fluid seal, desirably a gas seal.

The barrier member 12 at least partly contains liquid in the space 11between a final element of the projection system PS and the substrate W.A contactless seal 16 to the substrate W may be formed around the imagefield of the projection system so that liquid is confined within thespace between the substrate W surface and the final element of theprojection system PS. The space is at least partly formed by the barriermember 12 positioned below and surrounding the final element of theprojection system PS. Liquid is brought into the space below theprojection system and within the barrier member 12 by liquid inlet 13.The liquid may be removed by liquid outlet 13. The barrier member 12 mayextend a little above the final element of the projection system. Theliquid level rises above the final element so that a buffer of liquid isprovided. In an embodiment, the barrier member 12 has an inner peripherythat at the upper end closely conforms to the shape of the projectionsystem or the final element thereof and may, e.g., be round. At thebottom, the inner periphery closely conforms to the shape of the imagefield, e.g., rectangular, though this need not be the case.

In an embodiment, the liquid is contained in the space 11 by a gas seal16 which, during use, is formed between the bottom of the barrier member12 and the surface of the substrate W. The gas seal is formed by gas,e.g. air or synthetic air but, in an embodiment, N₂ or another inertgas. The gas in the gas seal is provided under pressure via inlet 15 tothe gap between barrier member 12 and substrate W. The gas is extractedvia outlet 14. The overpressure on the gas inlet 15, vacuum level on theoutlet 14 and geometry of the gap are arranged so that there is ahigh-velocity gas flow 16 inwardly that confines the liquid. The forceof the gas on the liquid between the barrier member 12 and the substrateW contains the liquid in a space 11. The inlets/outlets may be annulargrooves which surround the space 11. The annular grooves may becontinuous or discontinuous. The flow of gas 16 is effective to containthe liquid in the space 11. Such a system is disclosed in U.S. Pat.application publication No. US 2004-0207824.

Other arrangements are possible and, as will be clear from thedescription below, an embodiment of the present invention may use anytype of localized liquid supply system. An embodiment of the inventionis particularly relevant to use with any localized liquid supply systemsas the liquid supply system.

FIG. 6 illustrates a barrier member 12 which is part of a liquid supplysystem. The barrier member 12 extends around the periphery (e.g.,circumference) of the final element of the projection system PS suchthat the barrier member (which is sometimes called a seal member) is,for example, substantially annular in overall shape. The projectionsystem PS may not be circular and the outer edge of the barrier member12 may also not be circular so that it is not necessary for the barriermember to be ring shaped. The barrier has an opening through which theprojection beam may pass out from the final element of the projectionsystem PS. Thus, during exposure, the projection beam may pass throughliquid contained in the opening of the barrier member and onto thesubstrate W.

The function of the barrier member 12 is at least partly to maintain orconfine liquid in the space between the projection system PS and thesubstrate W so that the projection beam may pass through the liquid. Thetop level of liquid is simply contained by the presence of the barriermember 12.

The immersion liquid is provided to the space 11 by the barrier member12 (thus the barrier member may be considered to be a fluid handlingstructure). A passageway or flow path for immersion liquid passesthrough the barrier member 12. Part of the flow path is comprised by achamber 26. The chamber 26 has two side walls 28, 22. Liquid passesthrough the first side wall 28 into chamber 26 from chamber or outlet 24and then through the second side wall 22 into the space 11. A pluralityof outlets 20 provide the liquid to the space 11. The liquid passesthrough through holes 29, 20 in side walls 28, 22 respectively prior toentering the space 11. The location of the through holes 20, 29 may berandom.

A seal is provided between the bottom of the barrier member 12 and thesubstrate W. In FIG. 6 a seal device is configured to provide acontactless seal and is made up of several components. Radiallyoutwardly from the optical axis of the projection system PS, there isprovided a (optional) flow control plate 50 which extends into the space(though not into the path of the projection beam) which helps maintainsubstantially parallel flow of the immersion liquid out of outlet 20across the space. The flow control plate 50 has through holes 55 in itto reduce the resistance to movement in the direction of the opticalaxis of the barrier member 12 relative to the projection system PSand/or substrate W.

Radially outwardly of the flow control plate 50 on the bottom surface ofthe barrier member 12 may be an extractor assembly 70 to extract liquidfrom between the barrier member 12 and the substrate W and/or thesubstrate table WT. The extractor may operate as a single phase or as adual phase extractor.

Radially outwardly of the extractor assembly 70 may be a recess 80. Therecess is connected through an inlet 82 to the atmosphere. The recess isconnected via an outlet 84 to a low pressure source. Radially outwardlyof the recess 80 may be a gas knife 90. An arrangement of the extractor,recess and gas knife is disclosed in detail in U.S. Pat. applicationpublication No. US 2006/0158627.

The extractor assembly 70 comprises a liquid removal device or extractoror inlet such as the one disclosed in U.S. Pat. application publicationNo. US 2006-0038968. Any type of liquid extractor may be used. In anembodiment, the extractor assembly or liquid removal device 70 comprisesan inlet which is covered in a porous material 75 which is used toseparate liquid from gas to enable single-liquid phase liquidextraction. A chamber 78 downstream of the porous material 75 ismaintained at a slight under pressure and is filled with liquid. Theunder pressure in the chamber 78 is such that the meniscuses formed inthe holes of the porous material prevent ambient gas from being drawninto the chamber 78 of the extractor assembly 70. However, when theporous surface 75 comes into contact with liquid there is no meniscus torestrict flow and the liquid can flow freely into the chamber 78 of theextractor assembly 70.

During use (e.g., during the time that the substrate moves under thebarrier member 12 and projection system PS), a meniscus 320 extendingbetween the substrate W and the barrier member 12 is provided.

Although not specifically illustrated in FIG. 6 , the liquid supplysystem has an arrangement to deal with variations in the level of theliquid. This is so that liquid which builds up between the projectionsystem PS and the barrier member 12 can be dealt with and does notspill.

A substrate W is normally positioned in a recess (e.g. a substratesupporting area) within the substrate table WT. In order to account forvariations in the width (e.g., diameter) of the substrate W, the recessis usually made a little larger than the maximum likely size of thesubstrate W. Therefore, there exists a gap between the edge of thesubstrate and the substrate table W. With all arrangements for providingliquid, there may be a difficulty in the treatment of the gap 5 betweenthe substrate and the substrate table. This is because liquid can enterthis gap 5. It is desirable to remove liquid from the gap 5 to preventit from working its way under the substrate. It is also desirable toprevent bubbles of gas entering the immersion liquid from the gap 5. Forthis purpose an inlet may be provided below the gap between the edge ofthe substrate and substrate table. The inlet is connected to anunderpressure source so that liquid and/or gas can be removed from thegap 5.

FIG. 7 is a schematic cross-section through a substrate table WT and asubstrate W. The gap 5 exists between an edge of the substrate W and anedge of the substrate table WT. The gap 5 is at an outer area or edge ofa recess in which the substrate is placed during imaging. The substrateW can be supported on a substrate supporting area of the substrate tableWT.

In order to deal with the liquid entering that gap, at least one drain10, 17 may be provided at the edge of the substrate W to remove anyliquid which enters the gap 5. In the embodiment of FIG. 7 , two drains10, 17 are illustrated though there may be only one drain or there couldbe more than two drains.

The primary function of the first drain 10 is to prevent bubbles of gasfrom entering the liquid 11 of the liquid supply system 12. Any suchbubbles can deleteriously affect the imaging of the substrate W. Thesecond drain 17 may be provided to prevent any liquid which finds itsway from the gap 5 to underneath the substrate W from preventingefficient release of the substrate W from the substrate table WT afterimaging. As is conventional, the substrate W is held by a pimple tableor burl plate 30 comprising a plurality of projections 32 called burls.An underpressure applied between the substrate W and the substrate tableWT by the pimple table 30 ensures that the substrate W is held firmly inplace. The provision of the second drain 17 under the pimple table 30reduces or eliminates problems which may occur due to liquid finding itsway underneath the substrate W.

The first drain 10 removes liquid by way of an underpressure. That is,the first drain 10 is connected via outlet 142 to an underpressuresource. This underpressure source effectively removes any liquid whichenters the drain.

The exact geometry of the first drain 10 is not important. Typically,the first drain 10 comprises an inlet 110 which puts a chamber 140 intofluid communication with the gap 5. The chamber 140 may be annular, forexample. The outlet(s) 142 is in fluid communication with the chamber140.

The second drain 17 will now be described. An outlet 95 of the seconddrain 17 is held at an under pressure (e.g. 0.6 bar) which is a littlelarger than the under pressure (e.g. 0.5 bar) of the pimple table 30.This ensures that there is a flow of gas from the pimple table 30 aswell as from the gap 5 to the outlet 95. In an alternative embodiment,the second drain 17 can be held at an over pressure. In this case thereis a flow of gas out of the outlet 95 towards the gap 5. Combined withcapillary pressure this can be used to reduce or prevent immersionliquid getting into the pimple table 30.

As can be seen, two projections 91 and 92 are provided underneath thesubstrate W. The radially outer projection 91 is a so-called “wet seal”and is likely to have immersion liquid passing between it and the bottomsurface of the substrate W. The radially inner projection 92 is a dryseal and only gas is likely to pass between it and the substrate W.

Between the two projections 91, 92 is a channel 93 which leads to achamber 94. The chamber 94 is in fluid communication with the outlet 95which is connected to the under pressure source. More detail of thissecond drain 17 and of the first drain 10 can be found in U.S. Pat.application publication No. US 2008-0297744.

If gas is removed through the gap, then this may lead to undesirableevaporation of any liquid in the gap 5. This can in turn lead tolocalized cooling. Localized cooling is undesirable because it may leadto thermal contraction of the substrate table and thereby to possibleoverlay errors.

One way in which this phenomenon may be dealt with is to provide achannel for a heat transfer fluid in the substrate table WT. Thetemperature of the substrate table can be maintained constant in thisway. Additionally, as disclosed in U.S. Pat. publication No. US2008-0137055, a further heater may be used to heat in the vicinity ofthe inlet. Therefore, the extra thermal load which is generated at thatpoint may be compensated for by the use of that further heater.

FIG. 8 illustrates one such arrangement. FIG. 8 is a plan view of thesubstrate support area of a substrate table WT. The inlet 110 isindicated. A central channel 200 for heat transfer fluid is provided.The central channel 200 follows a path under the position of thesubstrate W. The path of the central channel 200 is such that an evenheating can be applied by passing a heating fluid through the channel200. The temperature of the heat transfer fluid entering the channel 200is detected by a first temperature sensor 210. The temperature of heattransfer fluid exiting the channel 200 is to be detected by a secondtemperature sensor 220. A third temperature sensor 230 may be providedin the channel 200 to detect the temperature at a local point. Acontroller can be provided with data from the temperature sensors 210,220, 230 and can control the temperature of the heat transfer fluidusing a heater 240 which is used to heat heat transfer fluid prior tothe heat transfer fluid entering the channel 200.

In order to deal with the excessive cooling which can be generated bythe drain 10, a heating element 250 may be provided. The heating element250 is a single heating element which is adjacent the inlet 110 andextends around the periphery (e.g., circumference) of the inlet 110.

The heating element 250 may be positioned underneath the chamber 140 oron either side of the chamber 140, as illustrated in FIG. 7 . There maybe other appropriate positions for the heater 250.

A fourth temperature sensor 260 is provided. The fourth temperaturesensor 260 is provided in the vicinity of the inlet 110. A controllercan use the information obtained from the fourth temperature sensor 260to control the power applied to the heating element 250.

Although the system illustrated in FIG. 8 does alleviate somedifficulties, particularly when a localized area liquid supply system isused, the cooling around the periphery of the inlet 110 is notnecessarily uniform. Therefore, the position of the fourth temperaturesensor 260 is significant. If the fourth temperature sensor 260 is in aposition which has experienced a large amount of local cooling, thenalthough that cooling may be compensated, other areas of the inlet 110may be heated too much. The difficulty with sensor 260 means that it maybe better to control the heating element 250 based on the temperaturedifference between the second and third temperature sensors 220 and 230.The controller uses this difference as a measure of the thermal load onthe substrate table edge. If on a part of the total periphery of thesubstrate table a thermal load is applied, the balancing heat load isapplied over the total periphery. As a result, the heating elementundercompensates the loaded area and disturbs the unloaded area. If forinstance 1 W is over ⅓^(rd) of the substrate table edge, this iscompensated with 1 W over the total edge. So, only 0.33 W of thatlocalized load is compensated, the other 0.66 W is disturbing the restof the edge. Even by the provision of further temperature sensors aroundthe inlet 110, this problem may not be alleviated.

The solution of FIG. 8 has the following short-comings: 1) theheater-sensor combination reaction time is too slow (long timeconstant). The heaters and sensors are glued to the substrate table WTresulting in relatively high contact resistances. 2) The heaters andsensors are only applied at the substrate table edge and not to its core(central portion), which provides a partial solution. 3) Waterconditioning is limited to a maximum flow which leads to a non-uniformtemperature distribution. Because the water channel is small incross-section and rather long the flow resistance is high. For highflows the pressure drop becomes too large, leading to non-uniformmechanical deformations of the wafer table itself. High flows also leadto high velocities and high dynamic forces, which lead to uncorrectabledisturbance forces. Any flow (not only the maximum flow) leads to anon-uniform temperature distribution. The water cools down from inlet tooutlet. This temperature difference results in non-uniformity. Thehigher the flow the lower the dT, of course. 4) Water conditioning canlead to uncorrectable dynamic disturbances because of pressure pulses.5) Water conditioning involves a ‘thick’ (10 mm), and therefore heavysubstrate table WT causing scan-up-scan-down problems.

In an embodiment heaters 400 and/or temperature sensors 500 are on asurface of the substrate table WT. The heaters 400 and/or temperaturesensors 500 may be on a surface adjacent (e.g. under) the substratesupporting area. One such surface is a surface of a burl plate 600.

A burl plate 600 of an embodiment is illustrated in FIG. 9 . The burlplate 600 is comprised of a plate with projections on an upper surfaceand on a lower surface. The projections on the upper surface are burls32 on which the substrate W, in use, is supported. The burls 34 on theunderside are for supporting the burl plate 600 on a surface of thesubstrate table WT.

In FIG. 7 the burl plate 30 is shown as an integral part of thesubstrate table WT and no burls equivalent to burls 34 or FIG. 9 arepresent.

In FIG. 9 the heater 400 and/or temperature sensor 500 are on a surfaceof the burl plate 600, formed between the burls 32, 34. The heater 400and/or temperature sensor 500 may be on a upwardly facing surface and/oron a downwardly facing surface of the burl plate 600.

In one embodiment the heater 400 and/or temperature sensor 500 areformed as a thin film. Therefore, the heater 400 and/or temperaturesensor 500 are attached directly to the surface without the use of anadhesive such as glue or solder etc. Thus, the heater 400 and/ortemperature sensor 500 are directly bonded to the surface, for exampledeposited on the surface. In one embodiment the heater 400 and/ortemperature sensor 500 are formed of platinum. If the burl plate 600 ismade of a conductive material (such as SiSiC), an insulating layerand/or a bonding layer may be deposited before the platinum heater 400and/or temperature sensor 500 is deposited. It may be necessaryadditionally to coat the heater 400 and/or temperature sensor 500 (withanother dielectric layer) once it has been deposited in order to ensureelectrical isolation of the heater 400 and/or temperature sensor 500 andprotection from moist gas which might otherwise create a short circuit.In an embodiment an additional insulating layer is provided over theheater 400 and/or temperature sensor 500 so heat goes into the surface.This results in more directing of heat into the body (e.g. burl plate600).

Normally the thin films have 4 layers in total. On top of the substratetable (e.g. burl plate 600) there is a bonding layer, then an isolatingdielectric layer, then the platinum layer and then again a dielectriclayer on top to avoid short-circuiting. To avoid electro-magneticinterference of the platinum lines there may be 2 extra shieldinglayers. The heaters and/or temperature sensors are thin, say below 100µm, preferably below 10 µm or even 1 µm thick.

The heater 400 and/or temperature sensor 500 are positioned adjacent thesubstrate supporting area. Because they are bonded directly to thesurface, heat is conducted to/from the heater 400 and/or temperaturesensor 500 to the material behind the surface quickly. If the surface towhich the heater 400 and/or temperature sensor 500 are applied is theburl plate, the transfer of heat to/from the substrate W is extremelyquick because of their proximity to the substrate W.

FIG. 10 shows, in plan, one embodiment of an arrangement of a pluralityof heaters 400 and/or temperature sensors 500. A plurality of heaters400 A-F and/or temperature sensors 500 A-F are elongate. They aresubstantially parallel in elongate direction and extend across thesubstrate supporting area from one edge to an opposite edge. The benefitof this arrangement will be explained with reference to FIG. 11 below.

Surrounding the central portion of the substrate supporting area wherethe heaters 400 A-F and/or temperature sensors 500 A-F are located, area plurality of edge heaters 410 A-L and/or temperature sensors 510 A-L.The edge heaters 410 A-L and/or temperature sensors 510 A-L are ofdifferent sizes around the edge of the substrate supporting area. Thesizes are to match the dimension in the direction of the heaters 400 A-Fand/or temperature sensors 500 A-F in the central portion.

The plurality of edge heaters is designed to do the job of the heatingelement 250 in FIG. 8 . That is, they are designed to compensate for thehigh evaporational loads around the edge of the substrate W as describedin connection with FIG. 7 . The edge heaters 410 A-L and/or temperaturesensors 510 A-L may be positioned on a surface of the burl plate 600 oron a different surface.

An embodiment of the present invention may be used on its own or incombination with an edge heater 250 as illustrated in FIG. 8 and/or apassage 230 adjacent the substrate supporting area for the passage of athermal conditioning fluid therethrough such as illustrated in FIG. 8 .Additionally, the heaters and/or temperature sensors of an embodiment ofthe invention may be employed in combination with a substrate table WTconditioned by a two-phase fluid. In such an embodiment a chamber isprovided in the body of the substrate table WT which is filled with afluid in both gaseous and liquid phases. Such a substrate tableconditioning system is described in U.S. Pat. application nos. US61/246,276, filed on 28 Sep. 2009 and US 61/246,268, filed on 28 Sep.2009, both hereby incorporated in their entirety by reference.

An advantage of an embodiment of the present invention is present bothfor heaters and for temperature sensors. The substrate table WT maycomprise one or the other or both. Both heaters and temperature sensorstake advantage of the fast thermal response of the thin film heatersand/or temperature sensors.

The arrangement of heaters and/or sensors illustrated in FIGS. 10 and 11, in particular, are also relevant to other types of heaters and/ortemperature sensors which are not necessarily thin films.

In one embodiment the heaters and/or temperature sensors are not on asurface but are enclosed within a component of the substrate table WT.The heaters and/or temperature sensors may be embedded in a top plate(e.g. a quartz plate) of the substrate table WT. The top plate maycomprise two sections, with the heaters and/or sensors embeddedtherebetween.

FIG. 11 shows an embodiment, in plan. In FIG. 11 the edge heaters 410A-L and/or temperature sensors 510 A-L are not present. It may not benecessary to include edge heaters, depending on the design of thesubstrate table WT at the edge of the substrate W. Such an embodiment isillustrated in FIG. 11 .

Also illustrated in FIG. 11 is a meander path 700 which the substratetable WT takes under the projection system PS. The general overallmotion of the meander path is illustrated by line 800.

As can be seen by comparing line 700 and line 800, whilst following thegeneral path 800 moving backwards and forwards in the X direction takesplace. Scanning in the Y direction is very fast. As a result, it can beseen that the substrate table WT moves fairly slowly from the top of thesubstrate (as illustrated) down to the bottom of the substrate along theY direction. For this reason the heaters and/or temperature sensors 400A-F, 500 A-F (and edge heaters and/or temperature sensors) are elongatein the X direction. The heaters and/or temperature sensors are elongatein a first direction. The first direction is orientated such that thelength of time a given heater and/or temperature sensor 400, 500 staysunder the projection system during imaging of the substrate W is greaterthan if the heater and/or sensor were orientated with its elongatedirection perpendicular to the first direction (in which case it wouldbe passed over several separate times during imaging of the wholesubstrate). In particular, the time that a given heater and/ortemperature sensor is under the projection system during imaging of thesubstrate is substantially maximized. In one embodiment this is done byensuring that the elongate direction of the heaters and/or temperaturesensors is parallel with the scanning direction. However, othergeometries may be more suitable for different scanning patterns. Thusduring imaging the substrate steps in the X direction along the topheater/temperature sensor 400A/500A while scanning in the Y direction.This results in the area at the top of the substrate receiving a heatload and this is sensed and compensated for by the top heater andtemperature sensor combination 400A/500A. The substrate then moves inthe Y direction to move the second heater/temperature sensor combination400B/500B under the projection system and scans in the Y direction. Theheat load is concentrated at that Y position and the sensor/heatercombination 400B/500B compensates accordingly. While stepping in the Xdirection any heat load is concentrated in that X direction. Inpositions along the Y axis away from the projection system, little heatload will be present.

An advantage of having elongate heaters and/or temperature sensors isthat then the number of heaters and/or temperature sensors can bereduced than would be the case if the heaters and/or temperature sensorswere made with an aspect ratio of substantially one (i.e. the samedimension in both the X and Y directions). The reduced number easescontrol and reduces the complexity of the system and in particularreduces the difficulty of connecting the heaters and/or temperaturesensors. As will be illustrated with reference to FIG. 12 , with theembodiment of FIGS. 10 and 11 , the heaters and/or temperature sensorsmay be connected to a controller at the edge of the burl plate 600relatively easily.

The plurality of heaters and/or temperature sensors are elongate insubstantially parallel directions.

FIG. 12 illustrates, in plan, a single integrated heater andcorresponding temperature sensor. Similar principles may be used foronly a heater or for only a temperature sensor. The heater andtemperature sensor are integrated in terms of heating and sensing thetemperature of the same area.

As illustrated in FIG. 12 , the heater and temperature sensor are formedas lines or wires. The lines or wires cover the area of the overallheater and/or temperature sensor. This is done by making the linesfollow a tortuous path. In the embodiment illustrated, the lines followa tortuous path between burls 32 but that is not necessarily the case.As illustrated in FIG. 12 , the line of the heater follows asubstantially parallel path to the line of the temperature sensor. Thetwo lines do not cross and weave their way in and out of the burls tocover as much area of the overall heater as is possible. The linesterminate at electrodes to allow connection to a control system.

A controller is provided. The controller attempts to maintain themeasured temperature at a given set point. The faster the response thebetter the performance which can be expected. The lower the thermal timeconstants, the smaller the net maximum temperature change which willoccur on the application of a heat load. The controller may control theheaters based on feedback from sensors. Feed forward control is possiblebased on the position of the liquid handling system 12 relative to thesubstrate table WT.

As depicted in FIG. 26 , an embodiment of the invention is to apply oneor more thin film platinum sensors and/or heaters on the top or bottomof the substrate table WT. In an embodiment the burl plate 600 ispositioned between the substrate table WT and the substrate W. In anembodiment, the thin film heaters 400 and/or temperature sensors 500 areapplied to the top of the burl plate 600. In an embodiment, the thinfilm heaters 400 and/or temperature sensors 500 are applied to thebottom surface of the burl plate 600. In an embodiment, the thin filmheaters 400 and/or temperature sensors 500 are applied to the bottomsurface of the substrate table WT.

The thin film heaters 400 and/or temperature sensors 500 may be appliedto the upper surface or lower surface of a sensor that is positioned onthe substrate table WT. FIG. 26 depicts a sensor 261 on the surface ofthe substrate table WT. The sensor 261 may be a dose sensor, anaberration sensor, an illumination sensor, a uniformity sensor or anaerial image sensor, for example. The sensor 261 may comprise an encodergrid plate to control the position of the substrate table WT. The sensor261 may comprise a protective plate 262 at its upper surface. Theprotective plate 262 may be formed of a glass. The one or more thin filmheaters 400 and/or temperature sensors 500 may be applied to the uppersurface and/or lower surface of the protective plate 262.

FIG. 29 depicts a lithographic apparatus comprising a substrate tableWT, a reference frame RF, a grating 50 and a sensor 20. The grating 50is attached to the substrate table WT or the reference frame RF. Thesensor 20 is attached to the other of the substrate table WT and thereference frame RF. FIG. 29 depicts the case in which the grating 50 isattached to the substrate table WT and the sensor 20 is attached to thereference frame RF.

The sensor 20 is to detect radiation diffracted and/or reflected by thegrating 50, thereby to measure the relative position between thesubstrate table WT and the reference frame RF. This is a type ofpositional measurement device used in a lithographic apparatus in whichthe grating 50 and sensor 20 are mounted on different objects which aremoveable relative to one another and whose relative position is desiredto be measured.

The thin film heaters 400 and/or temperature sensors 500 may be appliedto the upper surface or lower surface of the grating 50 and/or thesensor 20. The grating 50 may be formed on a plate of opticallytransparent material such as quartz or a glass-ceramic, for example.This plate may be termed an encoder grid plate. In this description, theterm grating 50 is understood to mean the encoder grid plate with agrating pattern formed thereon.

The thin film heaters 400 and/or temperature sensors 500 may be applieddirectly to the surface of the encoder grid plate. In an embodiment, thethin film heaters 400 and/or temperature sensors 500 are applieddirectly to the surface of the encoder grid plate that is exposed to theimmersion liquid. This is because the material of the plate, such asquartz or glass-ceramic, may have a relatively low thermal conductivity.Hence, local temperature changes due to thermal loads can be correctedmore quickly by positioning the thin film heaters 400 and/or temperaturesensors 500 on the exposed surface of the grating 50 than by positioningthe thin film heaters 400 and/or temperature sensors 500 on the rearside of the grating 50.

This controls the temperature of the grating 50 and/or sensor 20.Control of the temperature of the grating 50 and/or sensor 20 helps toreduce positional errors that would otherwise lead to overlay errors.The positional errors are caused by thermal deformation of a surface ofthe grating 50 and/or sensor 20. Such thermal deformation is caused by athermal load on the surface. A thermal load may be applied to thesurface if a liquid not the same temperature as the surface comes intocontact with the surface. For example, the liquid may evaporate, or inany case thermally equilibrate with the surface. This may be a problemfor the grating 50 as depicted in FIG. 29 because the grating 50 islocated on the upper surface of the substrate table WT and over whichthe fluid confinement structure 12 is located. The fluid confinementstructure 12 may become located over part or all of the grating 50during normal operation of the lithographic apparatus. Immersion liquidmay escape from the fluid confinement structure 12 and splash onto orremain on the grating 50 as a droplet. Of course, the same problem canoccur if the sensor 20 is positioned on the top surface of the substratetable WT and the grating 50 is positioned on the reference frame RF.

The grating 50 may comprise a grid plate and a grating surface formed onan under side of the grid plate. The purpose of this is to prevent thegrating surface itself from coming into contact with the immersionliquid.

Although in the above, an embodiment of the invention has been describedwith respect to the grating 50, the same advantages and mechanisms areapplicable to the temperature control of the sensor 20. For example,FIG. 30 depicts an embodiment in which the grating 50 is attached to thereference frame RF and the sensor 20 is attached to the substrate tableWT. The thin film heaters 400 and/or temperature sensors 500 may beapplied to the upper surface or lower surface of the sensor 20.

FIG. 31 depicts an embodiment in which additionally or alternatively tothe thin film temperature sensors 500, the lithographic apparatus maycomprise a non-contact temperature sensor 311. The non-contacttemperature sensor 311 may comprise an infrared temperature sensor. Inan embodiment, the non-contact temperature sensor 311 comprises an arrayof infrared sensors. The sensors may face towards the grating 50. Forexample, in an embodiment in which the grating 50 is positioned on anupper surface of the substrate table WT, the non-contact temperaturesensor 311 may face downward to the grating 50.

The non-contact temperature sensor 311 may be attached to the referenceframe RF as depicted in FIGS. 29 and 30 , or the contact temperaturesensor 311 may be attached to a measurement frame that is different fromthe reference frame RF.

The non-contact temperature sensor 311 may comprise a line of infraredsensors located above the substrate table WT. The non-contacttemperature sensor 311 measures the temperature of the grating 50 as thesubstrate table passes under the non-contact temperature sensor 311.This measurement may be performed during the alignment/focus measurementphase, the exposure phase or the substrate/substrate table swap phase,for example.

In an embodiment, the thin film heaters 400 and/or temperature sensors500 are applied to a surface of a measurement table.

Whether the thin film heaters 400 and/or temperature sensors 500 areapplied to a surface of the burl plate 600, the substrate table WT or asensor 261, the heaters 400 and/or temperature sensors 500 may beapplied by a number of different methods.

The heaters 400 and/or temperature sensors 500 may be glued on to theappropriate surface. The layer of glue between the heaters 400 and/ortemperature sensors 500 should be as thin as possible in order to reducethe contact resistance. The glue may comprise a polymer. The glue mayfurther comprise at least one metal and/or carbon fiber. The purpose ofthis is to make the glue electrically conductive and/or more thermallyconductive. The glue may be a pressure sensitive adhesive. This meansthat when pressure is applied to the glue, the layer of glue becomesthinner. The glue may also be termed an adhesive.

An alternative way to apply the thin film heaters 400 and/or temperaturesensors 500 to a surface is to form the network of heaters 400 and/orsensors 50 as a coating on the surface. The coating may be formed byusing either a positive photoresist or a negative photoresist.

In the case of using a positive photoresist, a coating of positivephotoresist is applied (e.g. sprayed) onto the surface. An isolationlayer, which may be made of SiO₂, may be applied prior to the positivephotoresist coating such that the isolation layer is between thepositive photoresist coating and a surface.

Once the positive photoresist coating has been applied to the surface,the coating is exposed at positions where the network of heaters 400and/or temperature sensors 500 is not to be applied, thereby to hardenthe positive photoresist at those positions. The remaining sections ofphotoresist are removed, thereby opening a gap where the thin film is tobe applied. The thin film, which may be made of platinum or an alloy oftitanium and platinum, for example, is applied to the surface and thephotoresist. The photoresist that remains on the surface is strippedvia, for example, an ultrasonic stripping technique to remove theunwanted sections of thin film. The result is a network of thin film inthe desired places.

A two-step photoresist method may be used in which two layers ofphotoresist are applied. The top layer of photoresist is exposed so asto be hardened in positions where the thin film is not to be applied.When the photoresist is developed by removing the section of photoresistthat is not hardened, the upper layer of photoresist overhangs the lowerlayer of photoresist such that the top layer of photoresist does nottouch the surface of the substrate W. This reduces defects in thephotoresist.

If a negative photoresist is used, a layer of negative photoresist iscoated onto the surface. This may be done by spraying. An isolationlayer may be applied before the negative photoresist layer. Thephotoresist is exposed in regions where the thin film is to be applied.These sections of photoresist are then removed. The thin film materialis disposed on the surface. The remaining sections of photoresist arestripped, thereby leaving the desired pattern of thin film material.

A further way to apply the thin film to the surface is to pre-applyadhesive to one side of the thin film material. The thin film withadhesive pre-applied to one surface may be termed a sticker. The stickermay then be applied to the surface. In the case of a sticker, the thinfilm material may be housed within an insulating material, such as apolyimide. In particular Kapton® may be used as the insulating materialfor the sticker.

It is desirable for the thin film to be directly bonded to the surfacein order to reduce the thermal resistance between the thin film and thesurface. However, an adhesive, which is desirably thermally conductive,may be used to apply the thin film to the surface.

The material of the thin film heaters 400 and/or temperature sensors 500may be platinum, or a platinum alloy. The thin film material maycomprise at least one of copper, aluminum, silver, gold and asemiconductor material, which may comprise a metal oxide and/or silicon.In the case of a sticker (i.e. thin film pre-applied with an adhesive,the thin film within an insulating housing), copper may in particular beused. The material for the thin film should be stable over time.

If the thin film is applied to the surface as a coating, a mask may beused to provide that the thin film material is applied to the desiredsections of the surface. In particular, a mask may be used when the oneor more thin film heaters 400 and/or temperature sensors 500 are appliedto a surface of the burl plate 600. FIG. 28 depicts a mask that may beused. FIG. 28 depicts thick lines indicating positions for the thin filmheaters 400 and thin lines indicating positions for the temperaturesensors 500. The mask is used to avoid the thin film material from beingdeposited undesirably on the burls 32.

FIG. 27 is a graph that illustrates the effectiveness of using one ormore thin film heaters 400 and/or sensors 500. The graph includes fourlines showing how the fingerprint size varies as a function of timedepending on the type of conditioning used to control the temperature ofthe system. The line formed of long, broken sections represents thesituation where no temperature conditioning is applied. The solid linerepresents the situation where a heat transfer fluid channel 200 (asdepicted in FIG. 8 ) is used to perform temperature conditioning. Thedot-chain line represents thin film conditioning, using a configurationas depicted in FIG. 9 . The line formed from short, broken sectionsrepresents ideal conditioning.

It is clear that the thin film conditioning has a result that is farcloser to the theoretical ideal conditioning than conditioning by a heattransfer fluid flowing in a heat transfer fluid channel 200 in thesubstrate table WT under the substrate supporting area.

An advantage of using thin film technology is that the sensing andheating lines are well connected to the surface, resulting in a very lowthermal contact resistance. Another advantage is that both sensors andheaters are made from the same material and that the complete layout ofmultiple sensors and heaters can be attached in one process step.

Because the thermal resistance is very low, thermal simulations of asubstrate table with thin film sensors and heaters show that substratetable temperatures can stay within mK’s making it an almost ideal tableconditioning concept. To cope for heating loads in one embodiment asubstrate table has heaters and sensors on the top as described above inrelation to FIGS. 10 and 11 and water conditioning in the middle. In oneembodiment the substrate table WT does not have water conditioning. Thisis possible for immersion machines were cooling loads are dominant. Inorder to minimize the number of sensors and heaters to be controlled,the following layout of FIG. 10 is suitable, with a 18 or 22 areas whicheach consist of 1 sensor-heater combination.

Of course, other layouts with more or less areas may be used. Becausescanning in X-direction takes typically less than 2 seconds for one row,one heater-sensor-combination over the full width of the substrate W issufficient. In the Y-direction more combinations may be required to copewith longer time scales, typically 10-20 seconds. The meander takes alonger time to move in Y-direction. The sensor-heater combination isable to react within 0.5 second, so field size in Y shall be limited.The multiple edge heater-sensor-combinations (12 or 16 areas,respectively) are provided to cope with the extra gap 5 evaporationloads. If these gap 5 evaporational loads are much reduced, then theedge combinations can be left out. Then the layout becomes as in FIG. 11.

The heater and sensor within one area shall be evenly distributed overthe total surface of its area for instance as illustrated in FIG. 12

Overlay performance increases because thermal cooling loads are measuredand corrected locally and within short time scales.

Doing away with water conditioning is advantageous because no waterhoses and no hydrodynamic pressure pulses are then present and thisallows for thinner substrate tables resulting in less scan-up scan-downproblems.

A further advantage of using one or more thin film heaters 400 and/ortemperature sensors 400 is that they have a lower mass than other typesof heaters or temperature sensors. This results in a substrate table WTthat has a lower mass than otherwise.

An embodiment of the invention is applicable to both 300 and 450 mmdiameter substrates W. For a 450 mm diameter substrate, the number ofsensors/heaters 400/500 will increase. The center sensors/heaters400/500 will be 450 mm in X and still 50 mm in Y, resulting in 9sensors/heaters 400/500 in Y, while for a 300 mm diameter substrate,there are 6 sensors/heaters 400/400 in Y. The edge sensors/heaters410/510 will get a similar pattern to the 300 mm diameter substrateresulting in 21 or 25 sensors/heaters 410/510 (i.e., the 300 mm diametersubstrate may have 18 or 22 sensors/heaters).

The number of heaters and/or temperature sensors in the center portionof the substrate supporting area may in one embodiment be only one (forexample covering a large proportion of the area) for global temperaturecorrection. In another embodiment a ‘check-board’ with manysensors/heaters 400/500 (for instance 1 sensor/heater 400/500 per diesize 26 mm x 32 mm) of heaters and/or temperature sensors may bepresent, for local correction.

The temperature sensor and heater lines within one die are notnecessarily aligned with the die orientation. The line length, linewidth, burl pattern and wire connection points will determine thelayout.

The edge heaters and/or sensors may be within or outside of the burls ofthe burl plate 600 or on the side edge or on the substrate table ring.

The following are aspects of the invention:

-   a) optimized bands of integrated heater and/or temperature sensor:    variations are possible to the optimal arrangement of heater and/or    temperature sensor if the standard immersion hood path were to vary;-   b) having a heater across the table surface;-   c) having a sensor across the table surface;-   d) having a sensor and heater integrated with each other, over the    surface of the table;-   e) having the sensor and/or heater integrated with the burls;-   having the sensor and/or heater as a thin film;-   g) using an integrated sensor/heater with an existing wafer edge    heater, two phase table control, and/or internal fluid conditioning    system;-   i) that there are systems on one side or both of the substrate    support; and-   j) an optimal arrangement for integrating the sensors and the    heaters.

The heater 400 and/or temperature sensor 500 may be of any shape, inplan. FIG. 13 shows one example in which a heater and/or sensor 400, 500comprises a line forming a meandering path. A heater 400 and a sensor500 may be associated with one another (as for example, in FIG. 12 ).The shape, in plan, of the heater 400 and sensor 500 may or may not besubstantially the same.

FIG. 14 shows a further shape, in plan, of a sensor 500 and/or heater400. In the case of FIG. 14 the overall shape of the sensor 500 and/orheater 400, in plan, is that of concentric circles which are joinedtogether to form a circuit.

The heater/sensor 400/500 embodiments of FIGS. 13 and 14 can be formedof one line to form a heater 400 and an associated sensor 500 in theform of a self-regulating thermal system, as described below,particularly with reference to FIG. 19 or as a micro-electro-mechanicalsystem (MEMS) described below with reference to FIGS. 16 and 17 .

The embodiment of FIG. 15 is an embodiment in which the heater 400 andsensor 500 are separate lines and are both formed as concentricinterwoven circles.

The self-regulating system is a device that activates or deactivates aheater due to local change in temperature. This heater provides thedesired thermal compensation at the right place and at the right timewithout any external input apart from the local change in temperature.In general, there are two ways to make a self-regulating device: (i) aheater with a MEMS switch, (ii) a heater made of a self-regulatingmaterial that has a high non-linear relationship between itselectromagnetic (EM) properties and temperature.

These devices are only a few micrometers thick, and their manufacturingcan be done by advanced direct writing or thin film technologies such asmetal and dielectric deposition, photolithography, wet and dry etching,galvanic and electro-less plating, diffusion and ion implantation amongothers. Due to the reduction in size of self-regulating devices, theycan be placed easily on any configuration, number (in the order ofthousands), geometry or on any surface.

The system can be trimmed using laser adjustment by removing material,reshaping the actuators, or changing its material crystallinity (if thatis possible), among other methods. In the case of complex surfaces, theself-regulating system can be assembled first on a thin flat film andthen transferred onto the final surface.

The heater 400 and/or temperature sensor 500 may form a self-regulatingthermal system. That is, no control signals need to be provided to theheater 400 and no signals need to be received from the temperaturesensor 500 by a remote controller. Instead, a voltage is applied to theheater 400 and/or temperature sensor 500 which then compensates forlocal temperature variation without the need for a separate controller.

One form of self-regulating thermal system is a MEMS basedself-regulating heater described below with reference to FIGS. 16 and 17. A further form is an EM-temperature based self-regulating heaterdescribed with reference to FIGS. 18, 19 and 20 .

A MEMS heater 400 is a heater activated and/or deactivated by a MEMSsensor 500. In one embodiment the sensor 500 is a switch. The switch canbe made of a positive coefficient of thermal expansion material, or anegative coefficient of thermal expansion material, or a bi-metallicmaterial. FIG. 16 shows a MEMS based self-regulating heater 400 andsensor 500, in cross-section. FIG. 17 shows a detail of the temperaturesensor 500 of FIG. 16 .

In FIG. 16 a heater 400 is connected in series with a temperature sensor500. The temperature sensor 500 is in the form of a self-regulatingswitch. A material 600 with a positive or negative coefficient ofthermal expansion or a bi-metallic material operates the switch. Usefulmaterials for construction of the sensor include silicon, polysilicon ora silicon compound such as silicon nitride or a metal such as gold.Thermal expansion and/or contraction of the material 600 results in theswitch being open above or below a certain temperature (top figure ofFIG. 17 ) and the switch is conversely closed below or above the certaintemperature. Current runs through the heater 400 when the switch isclosed. In one embodiment when the heater 400 is connected to a powersupply, and a change in temperature occurs, for example during cooling,the MEMS switch closes the circuit. Then an electrical current flowsthrough the heater 400 and warms the surface on which the heater 400 isformed. As the temperature increases, the material 600 of the switchstarts to deform (expansion, contraction or bending depending on theselective material) until the switch is opened stopping current frompassing through the heater 400 and thereby stopping heating.

The geometry of the MEMS structure can vary depending on thefunctionality (for example to include an overheat protection and improvethe manufacturability of the switch). Desirably the MEMS switch isadjacent or inside the heater 400 layout in order to react quickly tothe temperature change produced by the heater 400. The embodiment ofFIG. 14 shows a position 700 which would be suitable for positioning ofthe MEMS sensor/switch when the embodiment of FIG. 14 is a MEMS basedself-regulating heater.

In one embodiment the self-regulating heater may be an EM-temperaturebased self-regulating heater. This embodiment has an advantage (alsopresent in the MEMS embodiment) that only a single line needs to beplaced on the surface.

A heater 400 made of a self-regulating material (for example asemi-conductive polymer) may also act as a sensor 500 and switch as itis deactivated or activated as its EM property changes in response tothe surrounding temperature. FIG. 18 shows an example in which theresistance (Y axis) of a self-regulating heater varies as a function oftemperature (along the X axis). Therefore, if an electricalEM-temperature based self-regulating heater is connected to a powersupply (for example of a fixed voltage), then under a change intemperature, for example during cooling, the electrical resistance ofthe self-regulating material decreases considerably. This process allowsa flow of electrical current through the heater thereby warming thesurface. The heat increases the temperature of the heater and itssurroundings thereby increasing the electrical resistance until thecurrent ceases completely at a given temperature. This situation stopsthe heating process.

The construction of an EM-temperature based self-regulating heater canbe made by placing on a surface a thermal and electrically conductivelayer 800, then a self-regulating material film 810 and an electricallyconductive but similarly isolating layer 820 on top, as illustrated inFIG. 19 .

An EM-temperature based self-regulating heater can have any shape, inplan. Indeed, the heater need not be in the form of a line and could bein the form of blocks as illustrated, in perspective view, in FIG. 20 .In FIG. 20 heater/temperature sensors which are comprised of anEM-temperature based self-regulating heater 420 are illustrated. Thecentral electrical connection 450 is common to all EM-temperatureself-regulating heaters 420 and two electrodes 460 on either side of theEM-temperature based self-regulating heaters 420 can be used to completethe electrical circuit.

A non uniform temperature on a substrate W, due to liquid evaporation,can be corrected by a self-regulating substrate table WT. Theself-heating devices can be placed on the upper or lower burl plate 600surface. Under the presence of cold spots, for example droplets,electrical heaters 400 closer to those zones will be self-activated tocompensate thermally the substrate by heat conduction through the burls.Only two wires are required to power the substrate table WT. This systemcan reduce considerably the weight of the substrate table WT whileincreasing its reliability due to multiple self-regulating heaters 400placed on it.

The heaters 400 and/or temperature sensors 500 are described above asbeing applied to a surface of the substrate table WT adjacent asubstrate W supporting area. However, an embodiment of the invention canbe applied to any surface of a lithographic apparatus, particularly aprojection apparatus, more particularly an immersion lithographicprojection apparatus. FIGS. 21 and 22 illustrate various differentlocations at which heaters and/or temperature sensors 400, 500 might beplaced in a lithographic apparatus.

FIG. 21 is a plan view of a substrate table WT. The position of heaters400 and temperature sensors 500 adjacent the substrate supporting areahave already been discussed. Other sites may be around any sensor 1000,particularly around the edge of any sensor 1000. This is because theremay be a gap between the edge of a sensor 1000 and the edge of thesubstrate table WT which is held at an underpressure to remove liquidfrom the gap and thereby can see a high evaporation loss. The sensor 100may be a transmission image sensor (TIS) or an ILIAS sensor, forexample. Another area may be a drain around a dummy substrate 1100. Thedummy substrate 1100 is used to close the bottom of a fluid handlingsystem 12, during, for example, substrate swap, by positioning the dummysubstrate 1100 under the projection system PS. Thereby the fluidhandling system 12 may be maintained on during, for example, substrateswap which is advantageous in terms of avoiding drying stains on thefinal element of the projection system PS. Another way in which it ispossible to maintain the fluid handling system 12 operational during,for example, substrate swap is to provide a swap bridge 1200 on thesubstrate table WT. The swap bridge 1200 is a surface which extends fromthe substrate table WT (optionally retractably) and provides a surfacewhich can move under the fluid handling system 12 while, for example, anew second substrate table WT replaces the first substrate table WT. Agap between the top surface of the substrate table WT and a top surfaceof the swap bridge 1200 may be provided with an under pressure source toremove any liquid which finds its way into the gap. This area may beprovided with heaters and/or sensors described herein, as well as thetop surface of the substrate table WT itself adjacent the swap bridge1200. During, for example, substrate swap, the swap bridge 1200 engageswith the second substrate table WT. A further area 1300 where a swapbridge 1200 will engage with a substrate table WT is also provided withan under pressure source to remove liquid between the gap between theswap bridge 1200 and substrate table WT. This area 1300 may be providedwith a heater and/or temperature sensor described herein.

FIG. 22 shows those areas mentioned above as well as a fluid handlingsystem 12 and a projection system PS. Surfaces of the fluid handlingsystem 12 which may make use of the heaters and/or temperature sensorsdescribed herein include any surface which comes into contact withimmersion liquid during use. These include an under surface 40 of thefluid handling system 12, an inside surface 42 which defines a space inwhich liquid is held between the final end of projection system PS andthe substrate W, in use as well as a top surface 44. The top surface 44may be in contact with immersion liquid and in particular with ameniscus of liquid extending between the fluid handling system 12 andthe final element of the projection system PS. As the position of thatmeniscus on the top surface 44 moves, evaporational loads can be appliedto the top surface 44 so that heaters and/or temperature sensors mayusefully be placed there. For similar reasons, heaters and/ortemperature sensors may be placed around the edge of the projectionsystem PS where the meniscus between the projection system PS and thefluid handling system 12 may be positioned or where splashes may occur.For example, the heaters and/or temperature sensors may be placed aroundthe outer edge of a final element of the projection system PS.

The thin film heaters 400 described above may be combined withtemperature sensors that measure the temperature of a single point on asurface, rather than take an average of a temperature over a portion ofthe surface. For example, FIGS. 23, 24 and 25 depict a temperaturesensor that is configured to measure the temperature of a single pointon a surface that may be used according to an embodiment of the presentinvention.

FIG. 23 depicts an embodiment of the invention. FIG. 23 depicts how atemperature sensor 500 may be attached to the channel 200 or to thesubstrate table WT. The part to which the temperature sensor 500 isattached is given the reference numeral 131. The temperature sensor 500is configured to measure the temperature of the part 131. The part 131may be, for example, the channel 200 or the substrate table WT. However,part 131 may be any surface of the lithographic apparatus. Thetemperature sensor 500 is on the surface of the part 131. Thetemperature sensor 500 is attached to the surface by a thermallyconductive paste 132.

The temperature sensor 500 may comprise a thermistor, or otherthermometer equipment. According to the construction depicted in FIG. 23, the temperature sensor 500 is pressed directly against the part 131.The thermally conductive paste 132 may be provided intermediate thetemperature sensor 500 and the part 131. The paste may be heatconductive glue. The temperature sensor 500 is connected to anelectrical assembly 134 via at least one lead 133. The electricalassembly 134 takes temperature readings from the temperature sensor 500.The electrical assembly 134 may be a PCB. In an embodiment, thetemperature sensor 500 is mounted directly onto the electrical assembly134 without the need of the lead 133.

A drawback of the construction depicted in FIG. 23 is that it can bedifficult to position the temperature sensor 500 at the precise locationwhere it is desired to measure the temperature. This is partly due tothe presence of the electrical assembly 134 on which the temperaturesensor 500 is mounted, or the presence of the lead 133 connecting thetemperature sensor 500 to the electrical assembly 134. A furtherdrawback is that the lead 133 puts pressure on the temperature sensor500. This can undesirably affect temperature measurement taken by thetemperature sensor.

The temperature sensor 500 may be made of a semiconductor material. Thetemperature sensor 500 is configured to measure the temperature at asingle location.

FIGS. 24 and 25 depict an alternative to the construction of FIG. 23 forattaching the temperature sensor 500 to a part 131. FIG. 24 depicts aside view of the construction. FIG. 25 depicts a plan view of theconstruction.

The temperature sensor 500, which may be a thermistor, is attached tothe part 131 at the location at which the temperature is to be measured.At this location, the part 131 is coated with an electrically conductivecoating 141. The temperature sensor 500 is connected to the electricalassembly 134 via the coating 141. The temperature sensor 500 is on thesurface of the part 131. The temperature sensor 500 is connected to thesurface via the coating 141. In an embodiment, the temperature sensor500 is connected to the surface via the coating 141 and a layer of glue132.

Desirably, the electrically conductive coating is thermally conductive.As is most clearly seen in FIG. 25 , the electrically conductive coating141 takes the form of a pattern. The purpose of the pattern of thecoating 141 is to allow the electrically conductive coating 141 to beconnected to the electrical assembly 134 at an appropriate position. Forexample, an appropriate position may be where there is more space forthe electrical assembly 134 or for the lead 133 to connect to theelectrical assembly 134. For this purpose, the coating 141 may compriseat least one elongate portion.

The electrically conductive coating 141 also provides electricalshielding to the part 131 and/or to the temperature sensor 500. In thisway, electrical shielding can be provided without any additionalproduction steps. Measurement signals from the temperature sensor 500can be read out via the electrical assembly 134, which may be connecteddirectly to the coating 141, or indirectly via a lead 133.

The temperature sensor 500 may be attached directly to the coating 141.The temperature sensor 500 may be embedded within the coating 141. In anembodiment, the temperature sensor 500 is connected to a coating 141 viaa bonding layer 132. The bonding layer 132 may be formed of a thermallyconductive adhesive (i.e. glue). The bonding layer 132 may be formed ofa material for soldering. Desirably, the bonding layer 132 is less than10 µm thick.

A gap 142 may be provided between the temperature sensor 500 and thecoating 141. The purpose of the gap 142 is to prevent short-circuiting.The coating 141 is formed of two coating sections. Each section acts asan electrode to provide power to the temperature sensor 500 and/orreceive signals from the temperature sensor 500. The gap 142 separatesthe two coating sections from each other. The gap 142 may be filled withan electrically insulating material.

The thickness of the coating is less than 10 µm, less than 5 µm, lessthan 3 µm, or between 0.2 and 2.0 µm.

The electrically conductive coating 141 may be made of platinum, or apredominately platinum alloy, for example. The coating 141 may compriseat least one of copper, aluminum, silver and gold.

The same principle of use a coating 141 as an intermediary between theelectrical assembly 134 and the temperature sensor 500 may be used inthe context of a heater 400 instead of the temperature sensor 500.

In an embodiment, the bonding layer 132 is not present. The temperaturesensor 500 may be deposited as a coating. In an embodiment, the coating141 and the temperature sensor 500 may have positions that areinterchanged from the positions described above. The temperature sensor500 may attach to the part 131 directly.

Although an embodiment of the present invention has been described abovewith reference to an immersion lithographic apparatus, this need notnecessarily be the case. Other types of lithographic apparatus maysuffer from uneven cooling (or heating) around the edge of a substrate.For example, in an EUV apparatus (extreme ultra-violet apparatus)heating due to the impingement of the projection beam can occur. Thiscan give a localized heating to the substrate rather in the same way asthe passage of the edge of substrate under the localized liquid supplysystem can give a cooling effect. If the heat transfer fluid in thechannel 200 is given a small negative temperature offset with respect tothe desired temperature in a normal operating condition, all the heaterscan be on to obtain the desired temperature. A local cooling load canthen be applied by switching a heater off. In this circumstance it maybe that the localization of the heaters only at the edge of thesubstrate is too limited and that heaters may be additionally oralternatively be placed at different radial distances from the center ofthe substrate supporting area. However, the same principles as describedabove apply in this case also.

Therefore, as can be seen, an embodiment of the present invention can beimplemented in many types of immersion lithographic apparatus. Forexample, an embodiment of the invention may be implemented in an I-linelithographic apparatus.

In an aspect, there is provided a lithographic apparatus comprising aheater and/or temperature sensor on a surface.

In an embodiment, the surface is a surface of at least one selectedfrom: a substrate table configured to support a substrate on a substratesupporting area, a fluid handling system, a projection system, a surfaceof a grating or a sensor of a positional measurement device, and/or aswap bridge.

In an embodiment, the surface is a surface on a substrate tableconfigured to support a substrate on a substrate supporting area whichis: adjacent the substrate supporting area, or adjacent a sensor oradjacent a swap bridge.

In an embodiment, the lithographic apparatus further comprises a burlplate to support the substrate, wherein the surface on which the heaterand/or temperature sensor is formed is a surface of the burl plate.

In an embodiment, the heater and/or temperature sensor is formed on theburl plate between the burls.

In an embodiment, the surface is a surface of a final element of aprojection system.

In an embodiment, the heater and/or temperature sensor is a thin filmheater and/or temperature sensor.

In an embodiment, the heater and/or temperature sensor is directlybonded to the surface without use of an adhesive.

In an embodiment, the heater and/or temperature sensor is formed, inplan, as a line following a tortuous path.

In an embodiment, the heater and/or temperature sensor is formed ofplatinum

In an embodiment, the temperature sensor is connected to an electricalassembly to read measurements from the channel temperature sensorindirectly via an electrically conductive coating on the component towhich the temperature sensor is applied.

In an aspect, there is provided a lithographic projection apparatuscomprising a substrate table configured to support a substrate on asubstrate supporting area, the substrate table comprising a plurality ofheaters and/or temperature sensors adjacent a central portion of thesubstrate supporting area, the plurality of heaters and/or sensors beingelongate.

In an embodiment, the plurality of heaters and/or sensors are elongatein substantially parallel directions.

In an embodiment, the plurality of heaters and/or sensors extend acrossthe substrate supporting area from one edge to an opposite edge.

In an embodiment, the plurality of heaters are elongate in a firstdirection such that the length of time a given heater and/or temperaturesensor is under a projection system during imaging of a substrate isgreater than if the heater and/or sensor were oriented with its elongatedirection perpendicular to the first direction.

In an embodiment, the first direction is such that the length of time ismaximized.

In an embodiment, the plurality of heaters and/or temperature sensorsare comprised of a thin film.

In an embodiment, the lithographic apparatus further comprises a burlplate to support the substrate and wherein the plurality of heatersand/or temperature sensors are formed on a surface of the burl plate.

In an embodiment, the plurality of heaters and/or temperature sensorsare formed on the burl plate between the burls.

In an embodiment, the plurality of heaters and/or temperature sensorsare positioned on the top and/or bottom of the burl plate.

In an embodiment, the plurality of heaters and/or temperature sensorsare comprised of a line of material, in plan, which meanders in atortuous path, in plan.

In an embodiment, the substrate table further comprises plurality ofedge heaters adjacent different portions of an edge of the substratesupporting area and/or a chamber in the substrate table containing afluid in both gaseous and liquid phases and/or a passage adjacent thesubstrate supporting area for the passage of a thermal conditioningfluid therethrough.

In an embodiment, the substrate table comprises one heater and/ortemperature sensor per die on the substrate.

In an embodiment, the lithographic apparatus comprises a plurality ofthe heaters and a plurality of the temperature sensors.

In an embodiment, the plurality of heaters and plurality of temperaturesensors are, in plan, laid out in a two-dimensional grid.

In an embodiment, each heater is integrated with a correspondingtemperature sensor.

In an embodiment, each of the plurality of heaters is associated with acorresponding one temperature sensor of the plurality of temperaturesensors.

In an embodiment, a heater and an associated sensor form aself-regulating thermal system.

In an embodiment, the self-regulating thermal system is configured toactivate or deactivate the heater due to local change in temperature.

In an embodiment, the heater and associated sensor form amicro-electro-mechanical system.

In an embodiment, the associated sensor comprises a thermally activatedswitch.

In an embodiment, the heater and associated sensor are a self-regulatedheater having an electromagnetic property that varies as a function oftemperature such that a change in temperature results in a change inheat output at constant applied voltage.

In an aspect, there is provided a lithographic apparatus comprising asubstrate table configured to support a substrate on a substratesupporting area and comprising a heater and/or a temperature sensorwhich extends across the substrate supporting area from one edge to anopposite edge.

In an aspect, there is provided a lithographic apparatus comprising aheater and a temperature sensor integrated with each other.

In an embodiment, the heater and temperature sensor are formed on asurface.

In an embodiment, the lithographic apparatus further comprises a burlplate to support a substrate, and the surface on which the heater andtemperature sensor are formed is a surface of the burl plate.

In an aspect, there is provided a substrate table configured to supporta substrate on a substrate supporting area and a heater and/ortemperature sensor on a surface adjacent the substrate supporting area.

In an aspect, there is provided a method of compensating for a localheat load in an immersion lithographic projection apparatus the methodcomprising controlling a heater or using a signal from a temperaturesensor to compensate for a local heat load wherein the heater and/ortemperature sensor is on a surface.

In an embodiment, the heater and associated sensor form aself-regulating thermal system.

In an aspect, there is provided a lithographic apparatus comprising anelectrically conductive coating on a surface, and a heater and/ortemperature sensor connected to the coating.

In an embodiment, an electrical assembly is electrically connected tothe heater and/or temperature sensor via the coating.

In an embodiment, the heater and/or temperature sensor is connected tothe coating by a bonding layer.

In an embodiment, the bonding layer comprises an adhesive.

In an embodiment, the bonding layer comprises a material for soldering.

In an embodiment, an electrically insulating gap is provided between thesurface and the heater and/or temperature sensor.

In an embodiment, the heater and/or temperature sensor is embedded inthe coating.

In an embodiment, the coating comprises at least one of platinum,copper, aluminum, silver, gold and a semiconductor material.

In an embodiment, the heater and/or temperature sensor is substantiallywholly within the coating in plan view.

In an embodiment, the coating is patterned.

In an embodiment, the coating comprises at least one elongate portion.

In an embodiment, the coating is formed of at least two distinct coatingsections.

In an embodiment, the coating is an electrode.

In an embodiment, the coating is configured to provide electrical powerto, or receive electrical signals from, the heater and/or temperaturesensor.

In an embodiment, a thickness of the coating is less than 10 µm, lessthan 5 µm, less than 3 µm, or less than 1 µm.

Although specific reference may be made in this text to the use oflithographic apparatus in the manufacture of ICs, it should beunderstood that the lithographic apparatus described herein may haveother applications in manufacturing components with microscale, or evennanoscale features, such as the manufacture of integrated opticalsystems, guidance and detection patterns for magnetic domain memories,flat-panel displays, liquid-crystal displays (LCDs), thin-film magneticheads, etc. The skilled artisan will appreciate that, in the context ofsuch alternative applications, any use of the terms “wafer” or “die”herein may be considered as synonymous with the more general terms“substrate” or “target portion”, respectively. The substrate referred toherein may be processed, before or after exposure, in for example atrack (a tool that typically applies a layer of resist to a substrateand develops the exposed resist), a metrology tool and/or an inspectiontool. Where applicable, the disclosure herein may be applied to such andother substrate processing tools. Further, the substrate may beprocessed more than once, for example in order to create a multi-layerIC, so that the term substrate used herein may also refer to a substratethat already contains multiple processed layers.

The terms “radiation” and “beam” used herein encompass all types ofelectromagnetic radiation, including ultraviolet (UV) radiation (e.g.having a wavelength of or about 365, 248, 193, 157 or 126 nm).

The term “lens”, where the context allows, may refer to any one orcombination of various types of optical components, including refractiveand reflective optical components.

While specific embodiments of the invention have been described above,it will be appreciated that the invention may be practiced otherwisethan as described. For example, the embodiments of the invention maytake the form of a computer program containing one or more sequences ofmachine-readable instructions describing a method as disclosed above, ora data storage medium (e.g. semiconductor memory, magnetic or opticaldisk) having such a computer program stored therein. Further, themachine-readable instruction may be embodied in two or more computerprograms. The two or more computer programs may be stored on one or moredifferent memories and/or data storage media.

The controllers described above may have any suitable configuration forreceiving, processing, and sending signals. For example, each controllermay include one or more processors for executing the computer programsthat include machine-readable instructions for the methods describedabove. The controllers may also include data storage medium for storingsuch computer programs, and/or hardware to receive such medium.

One or more embodiments of the invention may be applied to any immersionlithography apparatus, in particular, but not exclusively, those typesmentioned above, whether the immersion liquid is provided in the form ofa bath, only on a localized surface area of the substrate, or isunconfined on the substrate and/or substrate table. In an unconfinedarrangement, the immersion liquid may flow over the surface of thesubstrate and/or substrate table so that substantially the entireuncovered surface of the substrate table and/or substrate is wetted. Insuch an unconfined immersion system, the liquid supply system may notconfine the immersion liquid or it may provide a proportion of immersionliquid confinement, but not substantially complete confinement of theimmersion liquid.

A liquid supply system as contemplated herein should be broadlyconstrued. In certain embodiments, it may be a mechanism or combinationof structures that provides a liquid to a space between the projectionsystem and the substrate and/or substrate table. It may comprise acombination of one or more structures, one or more liquid inlets, one ormore gas inlets, one or more gas outlets, and/or one or more liquidoutlets that provide liquid to the space. In an embodiment, a surface ofthe space may be a portion of the substrate and/or substrate table, or asurface of the space may completely cover a surface of the substrateand/or substrate table, or the space may envelop the substrate and/orsubstrate table. The liquid supply system may optionally further includeone or more elements to control the position, quantity, quality, shape,flow rate or any other features of the liquid.

The descriptions above are intended to be illustrative, not limiting.Thus, it will be apparent to one skilled in the art that modificationsmay be made to the invention as described without departing from thescope of the claims set out below.

1-20. (canceled)
 21. A substrate holder for use in a lithographicapparatus, the substrate holder comprising: a main body having a firstside of the main body and a second side of the main body opposite to thefirst side; a plurality of first burls at the first side of the mainbody and having end surfaces to support a substrate in the lithographicapparatus; a plurality of second burls at the second side of the mainbody; and at least part of a heater attached to an external surface ofthe main body at the second side, the at least part of the heaterconfigured to emit heat at the external surface.
 22. The substrateholder of claim 21, wherein the heater is located among the second burlssuch that end surfaces of the second burls are located further from theexternal surface than a first surface of the heater opposite to a secondsurface of the heater facing the external surface.
 23. The substrateholder of claim 21, further comprising one or more further heaters suchthat collectively at least part of each of the one or more furtherheaters surround the heater.
 24. The substrate holder of claim 23,wherein the one or more further heaters are located on the exterior ofthe main body.
 25. The substrate holder of claim 21, wherein the heateris an electric heater.
 26. The substrate holder of claim 21, furthercomprising a channel configured to pass heat transfer fluid through atleast part of the main body.
 27. A lithographic apparatus, comprising: asupport structure configured to support a patterning device; aprojection system arranged to project a beam patterned by the patterningdevice onto a substrate; and a substrate holder arranged to hold thesubstrate, the substrate holder being according to claim
 21. 28. Asubstrate holder for use in a lithographic apparatus, the substrateholder comprising: a main body having a first side of the main body anda second side of the main body opposite to the first side; a pluralityof first burls at the first side of the main body and having endsurfaces to support a substrate in the lithographic apparatus; aplurality of second burls at the second side of the main body; and atleast part of a heater located among the second burls.
 29. The substrateholder of claim 28, further comprising one or more further heaters suchthat collectively at least part of each of the one or more furtherheaters surround the heater.
 30. The substrate holder of claim 29,wherein the one or more further heaters are located on the exterior ofthe main body.
 31. The substrate holder of claim 28, wherein the heateris an electric heater.
 32. The substrate holder of claim 28, furthercomprising a channel configured to pass heat transfer fluid through atleast part of the main body.
 33. The substrate holder of claim 28,further comprising a temperature sensor configured to detect atemperature of at least part of the main body.
 34. A lithographicapparatus, comprising: a support structure configured to support apatterning device; a projection system arranged to project a beampatterned by the patterning device onto a substrate; and a substrateholder arranged to hold the substrate, the substrate holder beingaccording to claim
 28. 35. A substrate holder for use in a lithographicapparatus, the substrate holder comprising: a main body having a firstside of the main body and a second side of the main body opposite to thefirst side; a plurality of first burls at the first side of the mainbody and having end surfaces to support a substrate in the lithographicapparatus; a plurality of second burls at the second side of the mainbody; at least part of a heater at the second side; and one or morefurther heaters such that collectively at least part of each of the oneor more further heaters surround the heater.
 36. The substrate holder ofclaim 35, wherein the one or more further heaters are located on theexterior of the main body and away from the first side.
 37. Thesubstrate holder of claim 35, wherein the heater is an electric heater.38. The substrate holder of claim 37, wherein the one or more furtherheaters are one or more electric heaters.
 39. The substrate holder ofclaim 35, further comprising a channel configured to pass heat transferfluid through at least part of the main body.
 40. A lithographicapparatus, comprising: a support structure configured to support apatterning device; a projection system arranged to project a beampatterned by the patterning device onto a substrate; and a substrateholder arranged to hold the substrate, the substrate holder beingaccording to claim 35.